Currently, there is a severe deficiency in the packaging used in clean room sterilizing facilities. There is an abundance of packaging materials that are sterilizable and used in the medical industry for sterile presentation of surgical instruments. However, this packaging is generally inadequate for use in clean room sterilizing facilities. Many pharmaceutical and sterilizer clean rooms are class 100 or better, yet the items they sterilize are put in packaging produced in non-clean room environments. These items include a variety of pharmaceutical glassware, plasticware, containment and closure of devices for drugs, such as vials, syringes, rubber stoppers, and the like.
Presently, the sterilizable bag of choice for use in pharmaceutical clean rooms is a paper/polyester structure. The problem with this structure is the use of paper, even low shedding versions, introduces large quantities of particles into the environment and is not suitable for clean room work surfaces. Clearly, products can be only as clean, or as particulate free, as a package they are put in.
This paper/polyester sterilizable bag has several needs for improvement. The paper sheds a great deal of fiber particles and is unsuitable for many clean applications. The paper to polyester seal may be very weak and unable to carry large loads without failure. The paper tears easily when wet from being sterilized in steam autoclaves. This causes sterile quality assurance issues. Moreover, the paper only allows the effective transfer of steam in a narrow temperature range making sterilization questionable in steam autoclaves that are not tightly controlled.
Another packaging structure available is a polypropylene bag with a small TYVEK.RTM. window. This bag has only a heat tack weld between the TYVEK and the polypropylene resulting in weak seams that may fail. Also, the small window requires a longer sterilization time, and there is an added risk of residual gas plumes when ethylene oxide (ETO) is used for sterilization.
Another structure for use in pharmaceutical clean rooms is a steel tray with a breather window that is usually made of spun bond polypropylene. Because of the small breather window, larger differential pressures are needed to drive either the gas or steam in and out of the package during sterilization cycles. Also, longer sterilization times and drying times are required. And, there is the added risk of residual gas plumes emanating from-the tray, which may be hazardous to employees. Moreover, the steel trays are expensive and not adaptable for use with a variety of articles.
Another structure that is commonly used for sterile presentation of surgical instruments is the TYVEK/polyester peelable pouch, also known as a "Chevron" pouch. This pouch has one whole side made of polyester or other polymer film and the opposing side made of TYVEK. This product also has several drawbacks in clean room applications. The seals between the TYVEK and polyester film are generally designed to be peelable. This means that the seals are weak and may fail when carrying a load, especially after being sterilized. Even during sterilization, the seals may "blow out" if excessive pressure differentials are used, which limits the efficiency and lengthens the time required for sterilization cycles. Also, when the seals are peeled apart, TYVEK particles are generated in proximity to products inside the pouch. Finally, these products are generally not manufactured in clean room conditions and thus, have high particulate counts.
As may be understood from the above description, gas pervious materials are combined in these structures and adapted for gas or steam sterilization of the products contained inside. Fibrous polymer webs, such as spun-bonded polyolefins, and in particular a type of polyethylene known as "TYVEK 1059B or TYVEK 1073B", available from DuPont, Wilmington, Del., are useful for gas and steam sterilization. Such spun-bonded polyolefins are pervious to sterilizing gases such as ethylene oxide, steam, or dry heat while being impervious to bacteria and other contaminants. TYVEK 1059B and TYVEK 1073B, in particular, both have a pore size less than about 0.22 microns, which is sufficiently small to be impervious to bacteria and other major contaminants, while large enough to allow the flow of sterilizing gas and steam.
Although TYVEK has many advantages for use in this application, there are many drawbacks to avoid that caused many manufacturers to develop complicated structures. One drawback is the difficulty to make strong seals between TYVEK and other films without tearing or compromising the integrity of the TYVEK to bacteria infiltration. In obtaining-a strong heat seal or heat weld with TYVEK, when it is put under heat and pressure, it compresses fast and causes a stress point or a weak point that results in a failed seal. Another problem arises when attempting to make a strong seal by heat welding TYVEK to other materials that are not compatible of TYVEK due to different chemical structures and different melting temperatures. One way to avoid such problems is to make bags that have inherently weak seals or peelable seals. Therefore, the use of peelable structures is very common in the industry. The TYVEK layer can be coated with an adhesive or another polymer film to create a light tack weld to the underlying layer. Even un-coated, the TYVEK will create a weak tack weld with incompatible underlying films. But in these cases, the weld is not as strong as a hermetic, heat weld seal that would be desirable for pharmaceutical intermediate processing.
In attempting to obtain a strong seal between TYVEK and the opposing polymer film, there are numerous problems to overcome. Traditionally, most heat sealing machines apply heat both to top and bottom of the plastic film in between to heat and melt both the top layer and bottom layer together. However, when TYVEK is one of the layers, there is a lot of problems with getting a good hermetic seal. In a microscopic view, TYVEK is not a smooth film. There is a lot of variation in its gauge. Although it's typically produced to an average of 6.6 mil thickness, there is a lot of variation in the thickness because it's spun-bonded. There are areas where it is only 4 mils thick and there are other areas that may be 10 mils thick. In trying to make a seal, a uniform pressure and temperature is applied across the TYVEK. The high points of the surface come in close contact with the heating element but the low points do not. Portions of the TYVEK are compressed, with some portions heavily crushed and other portions slightly crushed. Often, there are tears and rips in the TYVEK from the excessive sheer stress, pressures and heat. Also, there are often pin holes created due to these variations in thickness, tearing and melted TYVEK flowing away from stress points. These pin holes and tears compromise the sterilizable bag's ability to resist the infusion of bacteria and contaminants after it has been sterilized. Even the strongest of these prior art seals with TYVEK has a pull resistance less than about four pounds per linear inch. Placing a heavy load of articles in these bags can pull apart that seal. Likewise, subjecting the bags to even normal differential pressures of--14 inches Hg during the sterilization cycles can cause the bag to inflate and pull apart or tear the seals.
Another problem with TYVEK used with prior art bags is that when the bags are manufactured with a peelable seal, the TYVEK can shed particles when the seal is opened, causing TYVEK fibers to get inside the bag and onto the sterilized clean product and articles inside. One should avoid particles from getting inside vials that are supposed to contain drugs for injection into human bodies. Moreover, because TYVEK has peaks and valleys and is not a smooth surface, a lot of particles like to stick in the valleys so that TYVEK has associated with it a lot of unclean particles that can shake loose and contaminate the articles being stored inside bags made with TYVEK. Again, the typical solution for this is to put a layer of perforated plastic film between the TYVEK and the article inside the bag. This ultimately requires the manufacture of a more complicated structure. And even the film that is between the TYVEK and the contents may not be clean. A lot of polymer films that are used in these structures generate high static charges that can attract minute particles which are difficult to dislodge except when clean articles having opposite charges are placed inside the bag. Then, the dirty particles jump off the polymer films and right onto the articles placed in the bag.
Therefore, there is a need for a sterilizable bag for use in this pharmaceutical secondary processing market that is simple and has a large gas permeable area, yet is impervious to bacteria and other contaminants. The large area reduces the time of sterilization cycles, thereby reducing operating costs. This bag must also have a very low particulate count to keep the contaminants from being carried to the articles from the surface of the bag. Also, there is a need for these bags to have strong seals which can withstand high differential pressures in aggressive sterilization cycles, and contain large quantities of articles that may be placed in the bag and stored for long periods.